Read environment variable of azure app service in my angular OR Store variable/url at some where in app service and read easily in angular app

I am facing one challenge in my PAAS application. I have two app services

1. Angular App Service
2. Dot Net App Service

I need to create deployment slot for each app service. And requirement is that Angluar slot app service should call Dotnet slot app service not original dotnet app service.

Original angluar app service continue calls Original dotnet app service.

How can I achieve that with any configuration in app service or some where else

For example

1. Define url Variable in configuration of each angular app service and read in angular then one question raises:

   How to use/read environment variable of azure app service in angular?

2. Store variable/URL some where in app service and read easily in angular. is there any way to do that?